Astragalus polysaccharides enhance the immune response and resistance of grass carp against grass carp reovirus.

The present study aimed to reveal the effects of Astragalus membranaceus polysaccharide (APS) on antioxidant capacity, immune-related gene expression, and inhibition of grass carp reovirus (GCRV) proliferation in grass carp (Ctenopharyngodon idella). Grass carps were fed experimental diets containing either 0.0% or 0.2% APS for 40 days. The results showed that APS supplementation significantly enhanced antioxidant capacity, as evidenced by increased activities of total antioxidant capacity (T-AOC), superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPX). Moreover, APS upregulated immune-related parameters, including immunoglobulin M (IgM), complement 3 (C3), complement factor B (Bf), mannose-binding lectin (MBL), lysozyme (LSZ), and C-X-C motif chemokine 13 (CXCL13), and modulated the expression of inflammatory cytokines such as interleukin 1β (IL-1β), tumor necrosis factor α (TNF-α), transforming growth factor β1 (TGF-β1), and interleukin 10 (IL-10). Furthermore, APS feeding markedly induced the expression of antiviral genes, including interferons (IFNs), interferon regulate factors (IRFs), and interferon stimulate genes, (ISGs)in the spleen, kidney, liver, and head kidney. Following intraperitoneal challenge with GCRV, the survival rate of the APS-treated group (76.67%) was significantly higher than that of the control group (43.33%). In addition, APS supplementation substantially reduced the relative protein levels of virus protein 5 (VP5)and virus protein 7 (VP7)during GCRV infection. These findings suggest that dietary APS enhances resistance to GCRV in grass carp by promoting immune fuction and antiviral responses. Collectively, our results demonstrate that APS effectively boosts immune activity and improves capacity of grass carp to combat GCRV infection. This study provides a theoretical basis and practical reference for the application of APS in the prevention and control of fish diseases.